(ii) To find the proportion of winter days with a minimum temperature below zero, we standardize the variable:

\(z = \frac{0 - \mu}{2\mu} = -0.5\)

The probability \(P(z < -0.5) = 1 - 0.6915 = 0.309\) or 30.9%.

(iii) To find how many of the 70 days have a temperature more than three times the mean:

\(z = \frac{3\mu - \mu}{2\mu} = 1\)

The probability \(P(z > 1) = 1 - 0.8413 = 0.1587\).

Thus, the expected number of days is \(70 \times 0.1587 = 11.1\), so approximately 11 or 12 days.

(iv) Given the probability of the temperature being above 6 °C is 0.0735, we find \(\mu\):

\(z = 1.45\)

\(1.45 = \frac{6 - \mu}{2\mu}\)

Solving for \(\mu\), we get \(\mu = 1.54\).